FUNCTIONAL DOMAINS IN FLAVOBACTERIUM OKEANOKOITES (FOKI) RESTRICTION ENDONUCLEASE

Abstract: The present inventors have identified the recognition and cleavage domains of the FokI restriction endonuclease. Accordingly, the present invention relates to the DNA segments encoding the recognition and cleavage domains of the FokI restriction endonuclease, respectively. The 41 kDa N-terminal fragment constitutes the FokI recognition domain while the 25 kDa C-terminal fragment constitutes the FokI cleavage nuclease domain. The present invention also relates to hybrid restriction enzymes comprising the nuclease domain of the FokI restriction endonuclease linked to a recognition domain of another enzyme. Additionally, the present invention relates to the construction of two insertion mutants of FokI endonuclease.

Description: FUNCTIONAL DOMAINS IN FLAVOBACTERIDM OKΣANOKOITES (FO I) RESTRICTION ENDONUCLEASE BACKGROUND OF THE INVENTION 1. Field of the Invention: The present invention relates to the Fokl restriction endonuclease system. In particular, the present invention relates to DNA segments encoding the separate functional domains of this restriction endonuclease system. The present invention also relates to the construction of two insertion mutants of Fokl endonuclease. 2. Background Information: Type II endonucleases and modification methylases are bacterial enzymes that recognize specific sequences in duplex DNA. The endonuclease cleaves the DNA while the methylases methylates adenine or cytosine residues so as to protect the host-genome against cleavage [Type II restriction and modification enzymes. .In Nucleases (Eds. Modrich and Roberts) Cold Spring Harbor Laboratory, New York, pp. 109-154, 1982]. These restriction- modification (R-M) systems function to protect cells from infection by phage and plasmid molecules that would otherwise destroy them. As many as 2500 restriction enzymes with over 200 specificities have been detected and purified (Wilson and Murray, Annu. Rev. Genet. 25:585-627, 1991). The recognition sites of most of these enzymes are 4-6 base pairs long. The small size of the recognition sites is beneficial as the phage genomes are usually small and these small recognition sites occur more frequently in the phage. Eighty different R-M systems belonging to the Type IIS class with over 35 specificities have been identified. This class is unique in that the cleavage site of the enzyme is separate from the recognition sequence. Usually the distance between the recognition site and the cleavage site is quite precise (Szybalski et al., Gene. 100:13-26, 1991). Among all these enzymes, the Fokl restriction endonuclease is the most well characterized member of the Type IIS class. The Fokl endonuclease (RFokl) recognizes asymmetric pentanucleotides in double-stranded DNA, 5' GGATG-3' (SEQ ID NO: 1) in one strand and S'-CCTAC-S' (SEQ ID NO: 2) in the other, and introduces staggered cleavages at sites away from the recognition site (Sugisaki et al., Gene 16:73-78; 1981). In contrast, the Fokl methylase (MFokl) modifies DNA thereby rendering the DNA resistant to digestion by Fokl endonuclease. The Fokl restriction and modification genes have been cloned and their nucleotide sequences deduced (Kita et al., J. of Biol. Chem.. 264:575-5756, 1989). Nevertheless, the domain structure of the Fokl restriction endonuclease remains unknown, although a three domain structure has been suggested (Wilson and Murray, Annu. Rev. Genet. 25:585-627, 1991) . SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide isolated domains of Type IIS restriction endonuclease. It is another object of the present invention to provide hybrid restriction enzymes which are useful for mapping and sequencing. An additional object of the present invention is to provide two insertion mutants of FOKI which have an increased distance of cleavage from the recognition site as compared to the wild- type enzyme. The polymerase chain reaction (PCR) is utilized to construct the two mutants. Various other objects and advantages of the present invention will become obvious from the drawings and the following description of the invention. In one embodiment, the present invention relates to a DNA segment encoding the recognition domain of a Type IIS endonuclease which contains the sequence-specific recognition activity of the Type IIS endonuclease or a DNA segment encoding the catalytic domain of a Type IIS endonuclease which contains the cleavage activity of the Type IIS endonuclease. In another embodiment, the present invention relates to an isolated protein consisting essentially of the N-terminus or recognition domain of the Fokl restriction endonuclease which protein has the sequence-specific recognition activity of the endonuclease or an isolated protein consisting essentially of the C-terminus or catalytic domain of the Fokl restriction endonuclease which protein has the nuclease activity of the endonuclease. In a further embodiment, the present invention relates to a DNA construct comprising a first DNA segment encoding the catalytic domain of a Type IIS endonuclease which contains the cleavage activity of the Type IIS endonuclease; a second DNA segment encoding a sequence-specific recognition domain other than the recognition domain of the Type IIS endonuclease; and a vector. In the construct, the first DNA segment and the second DNA segment are operably linked to the vector to result in the production of a hybrid restriction enzyme. In another embodiment, the present invention relates to a hybrid restriction enzyme comprising the catalytic domain of a Type IIS endonuclease which contains the cleavage activity of the Type IIS endonuclease linked to a recognition domain of an enzyme or a protein other than the Type IIS endonuclease from which the cleavage domain is obtained. In a further embodiment, the present invention relates to a DNA construct comprising a first DNA segment encoding the catalytic domain of a Type IIS endonuclease which contains the cleavage activity of the Type IIS endonuclease; a second DNA segment encoding a sequence-specific recognition domain other than the recognition domain of the Type IIS endonuclease; a third DNA segment comprising one or more codons, wherein the third DNA segment is inserted between the first DNA segment and the second DNA segment; and a vector. Preferably, the third segment contains four or seven codons. In another embodiment, the present invention relates to a procaryotic cell comprising a first DNA segment encoding the catalytic domain of a Type IIS endonuclease which contains the cleavage activity of the Type IIS endonuclease; a second DNA segment encoding a sequence-specific recognition domain other than the recognition domain of the Type IIS endonuclease; a third DNA segment comprising one or more codons, wherein the third DNA segment is inserted between the first DNA segment and the second DNA segment; and a vector. The first DNA segment and the second DNA segment are operably linked to the vector so that a single protein is produced. BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 shows sequences of the 5' and 3' primers used to introduce new translation signals into foklM and fokIR genes during PCR amplification. (SEQ ID NOs: 3-9) . SD represents Shine-Dalgarno consensus RBS for Escherichia coli (E. coli) and 7- bp spacer separates the RBS from the ATG start condon. The foklM primers are flanked by Ncol sites. The fokIR primers are flanked by BamHI sites. Start and stop codons are shown in bold letters. The 18-bp complement sequence is complementary to the sequence immediately following the stop codon of Mfokl gene. FIGURE 2 shows the structure of plasmids pACYCMfoJcJM, pRRSRfoJcJi? and pCB fokIR. The PCR- modified foklM gene was inserted at the NcoJ site of pACYC184 to form pACYCfofcJM. The PCR-generated fokIR gene was inserted at the BamHI sites of pRRS and pCB to form pRRS-ofcli? and pCBfo/cJ- , respectively. pRRS possesses a lac UV5 promoter and pCB contains a strong tac promoter. In addition, these vectors contain the positive retroregulator sequence downstream of the inserted fokIR gene. FIGURE 3 shows SDS (0.1%) - polyacrylamide (12%) gel electrophoretic profiles at each step in the purification of Fokl endonuclease. Lanes: 1, protein standards; 2, crude extract from uninduced cells; 3, crude extract from cells induced with 1 mM IPTG; 4, phosphocellulose pool; 5, 50-70% (NH^gSO* fractionation pool; and 6, DEAE pool. FIGURE 4 shows SDS (0.1%) - polyacrylamide (12%) gel electrophoretic profiles of tryptic fragments at various time points of trypsin digestion of Fokl endonuclease in presence of the oligonucleotide DNA substrate, d-5'-CCTCTGGATGCTCTC- 3' (SEQ ID NO: 10): 5'-GAGAGCATCCAGAGG-3• (SEQ ID NO:11). Lanes: 1, protein standards; 2, Fokl endonuclease; 3, 2.5 min; 4, 5 min; 5, 10 min; 6, 20 min; 7, 40 min; 8, 80 min; 9, 160 min of trypsin digestion respectively. Lanes 10-13: HPLC purified tryptic fragments. Lanes: 10, 41 kDa fragment; 11, 30 kDa fragment; 12, 11 kDa fragment; and 13, 25 kDa fragment. FIGURE 5 shows the identification of DNA binding tryptic fragments of Fokl endonuclease using an oligo dT-cellulose column. Lanes: 1, protein standards, 2, Fokl endonuclease; 3, 10 min trypsin digestion mixture of Fokl - oligo complex; 4, tryptic fragments that bound to the oligo dT- cellulose column; 5, 160 min trypsin digestion mixture of Fokl - oligo complex; 6, tryptic fragments that bound to the oligo dT-cellulose column. FIGURE 6 shows an analysis of the cleavage properties of the tryptic fragments of Fokl endonuclease. (A) The cleavage properties of the tryptic fragments were analyzed by agarose gel electrophoresis. 1 μg of pTZ19R in lO M Tris.HCl (pH 8), 50mM NaCl, ImM DTT, and lOmM MgCl 2 was digested with 2 μl of the solution containing the fragments (tryptic digests, breakthrough and eluate respectively) at 37°C for 1 hr in a reaction volume of 10 μl. Lanes 4 to 6 correspond to trypsin digestion of Fok I- oligo complex in absence of MgCl 2 « Lanes 7 to 9 correspond to trypsin digestion of Fokl - oligo complex in presence of 10 mM MgCl 2 - Lanes: 1, 1 kb ladder; 2, pTZ19R; 3, pTZ19R digested with Fokl endonuclease; 4 and 6, reaction mixture of the tryptic digests of Fokl - oligo complex; 5 and 7, 25 kDa C-terminal fragment in the breakthrough volume; 6 and 9, tryptic fragments of Fokl that bound to the DEAE column. The intense bands at bottom of the gel correspond to excess oligonucleotides. (B) SDS (0.1%) - polyacrylamide (12%) gel electrophoretic profiles of fragments from the DEAE column. Lanes 3 to 5 correspond to trypsin digestion of Fokl - oligo complex in absence of MgCl 2 . Lanes 6 to 8 correspond to trypsin digestion of Fokl - oligo complex in presence of 10 mM MgCl 2 . Lanes: 1, protein standards; 2, Fokl endonuclease; 3 and 6 , reaction mixture of the tryptic digests of Fokl - oligo complex; 4 and 7, 25 kDa C-terminal fragment in the breakthrough volume; 5 and 8, tryptic fragments of Fokl that bound to the DEAE column. FIGURE 7 shows an analysis of sequence - specific binding of DNA by 41 kDa N-terminal fragment using gel mobility shift assays. For the exchange reaction, the complex (10 μl) was incubated with 1 μl of 32 P-labeled specific (or non-specific) oligonucleotide duplex in a volume of 20 μl containing 10 mM Tris.HCl, 50 mM NaCl and 10 mM MgCl 2 at 37°C for various times. 1 μl of the 5*- 32 P- labeled specific probe [d-5'-CCTCTGGATGCTCTC-3• (SEQ ID NO: 10): 5'-GAGAGCATCCAGAGG-3• (SEQ ID NO: 11)] contained 12 picomoles of the duplex and - 50 x 10 3 cpm. lμl of the 5'- 32 P-labeled non-specific probe [δ'-TAATTGATTCTTAA-S 1 (SEQ ID NO: 12):5'- ATTAAGAATCAATT-3 ' (SEQ ID NO: 13)] contained 12 picomoles of the duplex and - 25 x IO 3 cpm. (A) Lanes: 1, specific oligonucleotide duplex; 2, 41 kDa N-terminal fragment-oligo complex; 3 and 4, specific probe incubated with the complex for 30 and 120 min respectively. (B) Lanes: 1, non-specific oligonucleotide duplex; 2, 41 kDa N-terminal fragment-oligo complex; 3 and 4 non-specific probe incubated with the complex for 30 and 120 min respectively. FIGURE 8 shows SDS (0.1%) polyacrylamide (12%) gel electrophoretic profiles of tryptic fragments at various time points of trypsin digestion of Fokl endonuclease. The enzyme (200 μg) in a final volume of 200 μl containing 10 mM Tris.HCl, 50 mM NaCl and lOmM MgCl 2 was digested with trypsin at RT. The trypsin to Fokl ratio was 1:50 by weight. Aliquots (28 μl) from the reaction mixture removed at different time intervals and quenched with excess antipain. Lanes: 1, protein standards; 2, Fokl endonuclease; 3, 2.5 min; 4, 5.0 min; 5, 10 min; 6, 20 min; 7, 40 min; 8, 80 min; and 9,160 min of trypsin digestion respectively. FIGURE 9 shows the tryptic map of Fokl endonuclease (A) Fokl endonuclease fragmentation pattern in absence of the oligonucleotide substrate. (B) Fokl endonuclease fragmentation pattern in presence of the oligonucleotide substrate. FIGURE 10 shows the predicted secondary structure of Fokl based on its primary sequencing using the PREDICT program. (See SEQ ID NO:31) The trypsin cleavage site of Fokl in the presence of DNA substrates is indicated by the arrow. The KSELEEKKSEL segment is highlighted. The symbols are as follows: h, helix; s, sheet; and ., random coil. FIGURE 11 shows the sequences of the 5' and 3' oligonucleotide primers used to construct the insertion mutants of Fokl (see SEQ ID NO:32, SEQ ID NO:33, SEQ ID NO:34, SEQ ID NO:35, SEQ ID NO:36, SEQ ID NO:37, SEQ ID NO:38 and SEQ ID NO:39, respectively) . The four and seven codon inserts are shown in bold letters. The amino acid sequence is indicated over the nucleotide sequence. The same 3' primer was used in the PCR amplification of both insertion mutants. FIGURE 12 shows the SDS/PAGE profiles of the mutant enzymes purified to homogeneity. Lanes: 1, protein standards; 2, Fokl ; 3 , mutant Fokl with 4-codon insertion; and 4, mutant Fokl with 7-codon insertion. FIGURE 13 shows an analysis of the DNA sequence specificity of the mutant enzymes. The DNA substrates were digested in 10 mM Tris HCl, pH 8.0/50 mM NaCl/1 mM DTT/lOmM MgCl 2 at 37°C for 2 hrs. (A) Cleavage pattern of pTZ19R DNA substrate analyzed by 1% agarose gel electrophoresis. 2μg of pTZ19R DNA was used in each reaction. Lanes: l, l-kilobase (kb) ladder; 2, pTZ19R; 3, pTZ19R digested with Fokl ; pTZ19R digested with mutant Fokl with 4-codon insertion; and 5, pTZ19R digested with mutant Fokl with 7-codon insertion. (B) Cleavage pattern of 256 bp DNA substrate containing a single Fokl site analyzed by 1.5% agarose gel electrophoresis. lμg of radiolabeled substrates ( 32 P-labeled on individual strands) was digested as described above. The agarose gel was stained with ethidium bromide and visualized under UV light. Lanes 2 to 6 correspond to the 32 P-labeled substrate in which the 5•-CATCC-3 • strand is 32_p labeled. Lanes 7 to 11 correspond to the substrate in which the 5'-GGATG-3 1 strand is 32 P- labeled. Lanes: l, lkb ladder; 2 and 7, 32 P-labeled 250 bp DNA substrates; 3 and 8, 32 -P labeled substrates cleaved with Fokl ; 4 and 9, purified the laboratory wild-type Fokl ; 5 and 10, mutant Fokl with 4-codon insertion; 6 and 11, mutant Fokl with 7-codon insertion. (C) Autoradiograph of the agarose gel from above. Lanes: 2 to 11, same as in B. FIGURE 14 shows an analysis of the distance of cleavage from the recognition site by Fokl and the mutant enzymes. The unphosphorylated oligonucleotides were used for dideoxy DNA sequencing with pTZ19R as the template. The sequencing products (G, A, T, C) were electrophoresed on a 6% acrylamide gel containing 7M urea, and the gel dried. The products were then exposed to an x-ray film for 2 hrs. Cleavage products from the 100 bp and the 256 bp DNA substrates are shown in A and B, respectively. I corresponds to substrates containing 32 P-label on the 5'-GGATG-3 1 strand, and II corresponds to substrates containing 32 P-label on the δ'-CATCC-S 1 strand. Lanes: 1, Fokl ; 2, Fokl ; 3, mutant Fokl with 4- codon insertion; and 4, mutant Fokl with 7-codon insertion. FIGURE 15 shows a map of the cleavage site(s) of Fokl and the mutant enzymes based on the 100 bp DNA substrate containing a single Fokl site: (A) wild-type Fokl ; (B) mutant Fokl with 4-codon insertion; and (C) mutant Fokl with 7-codon insertion (see SEQ ID NO:40) . The sites of cleavage are indicated by the arrows. Major cleavage sites are shown by larger arrows. DETAILED DESCRIPTION OF THE INVENTION The present invention is based on the identification and characterization of the functional domains of the Fokl restriction endonuclease. In the experiments resulting in the present invention, it was discovered that the Fokl restriction endonuclease is a two domain system, one domain of which possesses the sequence-specific recognition activity while the other domain contains the nuclease cleavage activity. The Fokl restriction endonuclease recognizes the non-palindromic pentanucleotide 5'- GGATG-3' (SEQ ID NO: 1) :5'-CATCC-3• (SEQ ID NO: 2) in duplex DNA and cleaves 9/13 nucleotides downstream from the recognition site. Since 10 base pairs are required for one turn of the DNA helix, the present inventors hypothesized that the enzyme would interact with one face of the DNA by binding at one point and cleave at another point on the next turn of the helix. This suggested the presence of two separate protein domains, one for sequence-specific recognition of DNA and one for endonuclease activity. The hypothesized two domain structure was shown to be the correct structure of the Fokl endonuclease system by studies that resulted in the present invention. Accordingly, in one embodiment, the present invention relates to a DNA segment which encodes the N-terminus of the Fokl restriction endonuclease (preferably, about the N-terminal 2/3's of the protein) . This DNA segment encodes a protein which has the sequence-specific recognition activity of the endonuclease, that is, the encoded protein recognizes the non-palindromic pentanucleotide d-5'- GGATG-3'(SEQ ID NO: 1) :5'-CATCC-3' (SEQ ID NO: 2) in duplex DNA. Preferably, the DNA segment of the present invention encodes amino acids 1-382 of the Fokl endonuclease. In a further embodiment, the present invention relates to a DNA segment which encodes the C-terminus of the Fokl restriction endonuclease. The protein encoded by this DNA segment of the present invention has the nuclease cleavage activity of the Fokl restriction endonuclease. Preferably, the DNA segment of the present invention encodes amino acids 383-578 of the Fokl endonuclease. DNA segments of the present invention can be readily isolated from a biological samples using methods known in the art, for example, gel electrophoresis, affinity chromatography, poly erase chain reaction (PCR) or a combination thereof. Further, the DNA segments of the present invention can be chemically synthesized using standard methods in the art. The present invention also relates to the proteins encoded by the DNA segments of the present invention. Thus, in another embodiment, the present invention relates to a protein consisting essentially of the N-terminus of the Fokl endonuclease which retains the sequence-specific recognition activity of the enzyme. This protein of the present invention has a molecular weight of about 41 kilodaltons as determined by SDS polyacrylamide gel electrophoresis in the presence of 2-mercaptoethanol. In a further embodiment, the present invention relates to a protein consisting essentially of the C-terminus of the Fokl restriction endonuclease (preferably, the C-terminal 1/3 of the protein) . The molecular weight of this protein is about 25 kilodaltons as determined by SDS polyacrylamide gel electrophoresis in the presence of 2-mercaptoethanol. The proteins of the present invention can be isolated or purified from a biological sample using methods known in the art. For example, the proteins can be obtained by isolating and cleaving the Fokl restriction endonuclease. Alternatively, the proteins of the present invention can be chemically synthesized or produced using recombinant DNA technology and purified. The DNA segments of the present invention can be used to generate 'hybrid' restriction enzymes by linking other DNA binding protein domains with the nuclease domain of Fokl . This can be achieved chemically as well as by recombinant DNA technology. Such chimeric enzymes are useful for physical mapping and sequencing of genomes of various species, such as, humans, mice and plants. For example, such enzymes would be suitable for use in mapping the human genome. Such chimeric enzymes are also valuable research tools in recombinant DNA technology and molecular biology. Currently only 4-6 base pair cutters and a few 8 base pair cutters are available commercially. (There are about 10 endonucleases which cut >6 base pairs that are available commercially.) By linking other DNA binding proteins to the nuclease domain of Fokl new enzymes can be generated that recognize more than 6 base pairs in DNA. Accordingly, in a further embodiment, the present invention relates to a DNA construct and the hybrid restriction enzyme encoded therein. The DNA construct of the present invention comprises a first DNA segment encoding the nuclease domain of the Fokl restriction endonuclease, a second DNA segment encoding a sequence-specific recognition domain and a vector. The first DNA segment and the second DNA segment are operably linked to the vector so that expression of the segments can be effected thereby yielding a chimeric restriction enzyme. The construct can comprise regulatory elements such as promoters (for example, T7, taσ, trp and lac UV5 promoters) , transcriptional terminators or retroregulators (for example, stem loops) . Host cells (procaryotes such as E. coli) can be transformed with the DNA constructs of the present invention and used for the production of chimeric restriction enzymes. The hybrid enzymes of the present invention comprise the nuclease domain of Fokl linked to a recognition domain of another enzyme or DNA binding protein (such as, naturally occurring DNA binding proteins that recognize 6 base pairs) . Suitable recognition domains include, but are not limited to, the recognition domains of zinc finger motifs; homeo domain motifs; other DNA binding protein domains of lambda repressor, lac repressor, cro, gal4; DNA binding protein domains of oncogenes such as myc, j n ; and other naturally occurring sequence-specific DNA binding proteins that recognize >6 base pairs. The hybrid restriction enzymes of the present invention can be produced by those skilled in the art using known methodology. For example, the enzymes can be chemically synthesized or produced using recombinant DNA technology well known in the art. The hybrid enzymes of the present invention can be produced by culturing host cells (such as, HB101, RR1, RB791 and MM294) containing the DNA construct of the present invention and isolating the protein. Further, the hybrid enzymes can be chemically synthesized, for example, by linking the nuclease domain of the Fokl to the recognition domain using common linkage methods known in the art, for example, using protein cross- linking agents such as EDC/NHS, DSP, etc. While the Fokl restriction endonuclease was the enzyme studied in the following experiments, it is expected that other Type IIS endonucleases (such as, those listed in Table 2) will function using a similar two domain structure which one skilled in the art could readily determine based on the present invention. Recently, Stsl , a heteroschizomer of Fokl has been isolated from Streptococcus sanguis (Kita et al.. Nucleic Acids Research 20 (3)) 618, 1992). Stsl recognizes the same nonpalindromic pentadeoxyribonucleotide 5'-GGATG-3• :5'-CATCC-3• as Fokl but cleaves 10/14 nucleotides downstream of the recognition site. The -Stsl RM system has been cloned and sequenced (Kita et al.. Nucleic Acids Research 20 (16) 4167-72, 1992). Considerable amino acid sequence homology (r.30%) has been detected between the endonucleases, Fokl and Stsl . Another embodiment of the invention relates to the construction of two insertion mutants of Fokl endonuclease using the polymerase chain reaction (PCR) . In particular, this embodiment includes a DNA construct comprising a first DNA segment encoding the catalytic domain of a Type IIS endonuclease which contains the cleavage activity of the Type IIS endonuclease, a second DNA segment encoding a sequence-specific recognition domain other than the recognition domain of the Type IIS endonuclease, and a third DNA segment comprising one or more codons. The third DNA segment is inserted between the first DNA segment and the second DNA segment. The construct also includes a vector. The Type IIS endonuclease is Fokl restriction endonuclease. Suitable recognition domains include, but are not limited to, zinc finger motifs, homeo domain motifs, DNA binding domains of repressors, DNA binding domains of oncogenes and naturally occurring sequence-specific DNA binding proteins that recognize >6 base pairs. As noted above, the recognition domain of Fokl restriction endonuclease is at the amino terminus of Fokl endonuclease, whereas the cleavage domain is probably at the carboxyl terminal third of the molecule. It is likely that the domains are connected by a linker region, which defines the spacing between the recognition and the cleavage sites of the DNA substrate. This linker region of Fokl is susceptible to cleavage by trypsin in the presence of a DNA substrate yielding a 41-kDa amino- terminal fragment (The DNA binding domain) and a 25- kDa carboxyl-terminal fragment (the cleavage domain) . Secondary structure prediction of Fokl endonuclease based on its primary amino acid sequence supports this hypothesis (see Figure 10) . The predicted structure reveals a long stretch of alpha helix region at the junction of the recognition and cleavage domains. This helix probably constitutes the linker which connects the two domains of the enzyme. Thus, it was thought that the cleavage distance of Fokl from the recognition site could be altered by changing the length of this spacer (the alpha helix). Since 3.6 amino acids are required to form one turn of the alpha helix, insertion of either four codons or seven codons in this region would extend the pre¬ existing helix in the native enzyme by one or two turns, respectively. Close examination of the amino acid sequence of this helix region revealed the presence of two KSEL repeats separated by amino acids EEK (Figure 10) (see SEQ ID NO:21). The segments KSEL (4 codons) (see SEQ ID NO:22) and KSELEEK (7 codons) (see SEQ ID NO:23) appeared to be good choices for insertion within this helix in order to extend it by one and two turns, respectively. (See Examples X and XI.) Thus, genetic engineering was utilized in order to create mutant enzymes. In particular, the mutants are obtained by inserting one or more, and preferably four or seven, codons between the recognition and cleavage domains of Fokl . More specifically, the four or seven codons are inserted at nucleotide 1152 of the gene encoding the endonuclease. The mutants have the same DNA sequence specificity as the wild-type enzyme. However, they cleave one nucleotide further away from the recognition site on both strands of the DNA substrates as compared to the wild-type enzyme. Analysis of the cut sites of Fokl and the mutants, based on the cleavage of the 100 bp fragment, is summarized in Figure 15. Insertion of four (or seven) codons between the recognition and cleavage domains of Fokl is accompanied by an increase in the distance of cleavage from the recognition site. This information further supports the presence of two separate protein domains within the Fokl endonuclease: one for the sequence specific recognition and the other for the endonuclease activity. The two domains are connected by a linker region which defines the spacing between the recognition and the cleavage sites of the DNA substrate. The modular structure of the enzyme suggests it may be feasible to construct chimeric endonucleases of different sequence specificity by linking other DNA-binding proteins to the cleavage domain of the Fokl endonuclease. In view of the above-information, another embodiment of the invention includes a procaryotic cell comprising a first DNA segment encoding the catalytic domain of a Type IIS endonuclease which contains the cleavage activity of the Type IIS endonuclease, a second DNA segment encoding a sequence-specific recognition domain other than the recognition domain of the Type IIS endonuclease, and a third DNA segment comprising one or more codons. The third DNA segment is inserted between the first DNA segment and the second DNA segment. The cell also includes a vector. Additionally, it should be noted that the first DNA segment and the second DNA segment are operably linked to the vector so that a single protein is produced. The third segment may consist essentially of four or seven codons. The present invention also includes the protein produced by the procaryotic cell referred to directly above. In particular, the isolated protein consists essentially of the recognition domain of the Fokl restriction endonuclease, the catalytic domain of the Fokl restriction endonuclease, and amino acids encoded by the codons present in the third DNA segment. The following non-limiting Examples are provided to describe the present invention in greater detail. EXAMPLES The following materials and methods were utilized in the isolation and characterization of the Fokl restriction endonuclease functional domains as exemplified hereinbelow. Bacterial strains and plasmids Recombinant plasmids were transformed into E. coli RB791 i -^ cells which carry the lac i -l allele on the chromosome (Brent and Ptashne, PNAS USA. 78:4204-4208, 1981) or E. coli RRl cells. Plasmid pACYCfofcJM is a derivative of pACYC184 carrying the PCR-generated foklM gene inserted into Ncol site. The plasmid expresses the Fokl methylase constitutively and was present in RB791 cells (or RRl cells) whenever the fokIR gene was introduced on a separate compatible plasmid. The Fokl methylase modifies Fokl sites and provides protection against chromosomal cleavage. The construction of vectors pRRS and pCB are described elsewhere (Skoglund et al.. Gene. 88:1-5, 1990). Enzymes, biochemicals and oliσos Oligo primers for PCR were synthesized with an Applied Biosystem DNA synthesizer using cyanoethyl phosphoramidite chemistry and purified by reversed phase HPLC. Restriction enzymes were purchased from New England Biolabs. The DNA ligase IPTG were from Boehringer-Mannheim. PCR reagents were purchased as a Gene Amp Kit from Perkin-El er. Plasmid purification kit was from QIAGEN. Restriction enzyme assays Cells from a 5-ml sample of culture medium were harvested by centrifugation, resuspended in 0.5 ml sonication buffer [50 mM Tris.HCl (pH 8) , 14mM 2- mercaptoethanol] , and disrupted by sonication (3 x 5 seconds each) on ice. The cellular debris was centrifuged and the crude extract used in the enzyme assay. Reaction mixtures (10 μl) contained lOmM Tris.HCl (pH 8) , 10 mM MgCl 2 , 7 mM 2-mercaptoethanol, 50 μg of BSA, 1 μg of plasmid pTZ19R (U.S. biochemicals) and lμl of crude enzyme. Incubation was at 37°C for 15 min. tRNA (10 μg) was added to the reaction mixtures when necessary to inhibit non¬ specific nucleases. After digestion, 1 μl of dye solution (100 mM EDTA, 0.1% bro ophenol blue, 0.1% xylene cyanol, 50% glycerol) was added, and the samples were electrophoresed on a 1% agarose gel. Bands were stained with 0.5 μg ethidium bromide/ml and visualized with 310-nm ultraviolet light. SDS/PAGE Proteins were prepared in sample buffer and electrophoresed in SDS (0.1%)- polyacrylamide (12%) gels as described by Laemmli (Laem li, Nature. 222:680-685, 1970). Proteins were stained with coomassie blue. Example I Cloninσ of Fokl RM system The Fokl system was cloned by selecting for the modification phenotype. FlavoJacterium okeanokoites strain DNA was isolated by the method described by Caserta et al. (Caserta et al., J. Biol. Chem.. 262:4770-4777, 1987). Several Flavobacterium okeanokoites genome libraries were constructed in plasmids pBR322 and pUC13 using the cloning enzymes Pstl, BamHI and Bglll . Plasmid library DNA (10 μg) was digested with 100 units of Fokl endonuclease to select for plasmids expressing fokIM+ phenotype. Surviving plasmids were transformed into RRl cells and transformants were selected on plates containing appropriate antibiotic. After two rounds of biochemical enrichment, several plasmids expressing the foklM÷ phenotype from these libraries were identified. Plasmids from these clones were totally resistant to digestion by Fokl . Among eight transformants that were analyzed from the F. okeanokoites pBR322 Pstl library, two appeared to carry the foklM gene and plasmids from these contained a 5.5 kb Pstl fragment. Among eight transformants that were picked from F. okeanokoites pBR322 BamHI library, two appeared to carry the foklM gene and their plasmids contained ~ 18 kb BamHI fragment. Among eight transformants that were analyzed from the F. okeanokoites genome Bglll library in pUC13, six appeared to carry the foklM gene. Three of these clones had a 8 kb Bglll insert while the rest contained a 16 kb Bglll fragment. Plating efficiency of phage λ on these clones suggested that they also carried the fokIR gene. The clones with the 8-kb Bglll insert appeared to be most resistant to phage infection. Furthermore, the Fokl endonuclease activity was detected in the crude extract of this clone after partial purification on a phosphocellulose column. The plasmid, pUCfokIRM from this clone was chosen for further characterization. The 5.5 kb PstJ fragment was transferred to M13 phages and the nucleotide sequences of parts of this insert determined using Sanger's sequencing method (Sanger et al., PNAS USA. 74:5463-5467, 1977) . The complete nucleotide sequence of the Fokl RM system has been published by other laboratories (Looney et al.. Gene. 80:193-208, 1989; Kita et al.. Nucleic Acid Res.. 17:8741-8753, 1989; Kita et al-, J. Biol. Chem. 264:5751-5756. 1989). Example II Construction of an efficient overproducer clone of Fokl endonuclease using polvmerase chain reaction. The PCR technique was used to alter transcriptional and translational signals surrounding the fokIR gene so as to achieve overexpression in E. coli (Skoglund et al.. Gene. 88:1-5, 1990). The ribosome-binding site preceding the fokIR and foklM genes were altered to match the consensus E. coli signal. In the PCR reaction, plasmid pUCfoklRM DNA linearized with BamHI was used as the template. PCR reactions (100 μl) contained 0.25 nmol of each primer, 50 μM of each dNTP, 10 mM Tris.HCl (pH 8.3 at 25°C), 50 mM KCl, 1.5 mM MgCl 2 0.01% (W/V) gelatin, 1 ng of template DNA, 5 units of Taq DNA polymerase. The oligo primes used for the amplification of the fokIR and foklM genes are shown in Figure 1. Reaction mixtures (ran in quadruplicate) were overlayed with mineral oil and reactions were carried out using Perkin-Elmer-Cetus Thermal Cycler. Initial template denaturation was programmed for 2 min. Thereafter, the cycle profile was programmed as follows: 2 min at 37°C (annealing) , 5 min at 72°C (extension) , and 1 min at 94°C (denaturation) . This profile was repeated for 25 cycles and the final 72°C extension was increased to 10 min. The aqueous layers of the reaction mixtures were pooled and extracted once with 1:1 phenol/chloroform and twice with chloroform. The DNA was ethanol-precipitated and resuspended in 20 μl TE buffer [10 mM Tris.HCl, (pH 7.5), 1 mM EDTA]. The DNA was then cleaved with appropriate restriction enzymes to generate cohesive ends and gel-purified. The construction of an over-producer clone was done in two steps. First, the PCR-generated DNA containing the foklM gene was digested with Ncol and gel purified. It was then ligated into NσoJ-cleaved and dephosphorylated pACYC184 and the recombinant DNA transfected into E. coli RB791 ii or RRl cells made competent as described by Maniatis et al (Maniatis et al. , Molecular Cloning. A laboratory manual Cold Spring Harbor Laboratory. Cold Spring Harbor. NY. 1982) . After Tc selection, several clones were picked and plasmid DNA was examined by restriction analysis for the presence of foklM gene fragment in correct orientation to the chloramphenicol promoter of the vector (see figure 2) . This plasmid expresses Fokl methylase constitutively and then protects the host from chromosomal cleavage, when the fokIR gene is introduced into this host on a compatible plasmid. The plasmid DNA from these clones are therefore resistant to Fokl digestion. Second, the PCR-generated fokIR fragment was ligated into BamHI-cleaved and dephosphorylated high expression vectors pRRS or pCB. pRRS possesses a lac UV5 promoter and pCB containing the strong taσ promoter. In addition, these vectors contain the positive retroregulator stem-loop sequence derived from the crystal protein-encoding gene of Bacillus Thuringiensis downstream of the inserted fokIR gene. The recombinant DNA was transfected into competent E. COli RB791 i? [pACYCfo/Jtf] or RRl[pACYCfoJcDf]cells. After Tc and Ap antibiotic selection, several clones were picked and plasmid DNA was examined by restriction analysis for fokIR gene fragment in correct orientation for expression from the vector promoters. These constructs were then examined for enzyme production. To produce the enzyme, plasmid-containing RB791 i^ or RRl cells were grown at 37°C with shaking in 2x concentrated TY medium [1.6% tryptone, 1% yeast extract, 0.5% NaCl (pH 7.2)] supplemented with 20 μg Tc/ml (except for the pOCfoklRM plasmid) and 50 μg Ap/ml. IPTG was added to a concentration of 1 mM when the cell density reached 0.8. The cells were incubated overnight (12 hr) with shaking. As is shown in Figure 2, both constructs yield Fokl to a level of 5-8% of the total cellular protein. Examples III Purification of FoKl endonuclease A simple three-step purification procedure was used to obtain electrophoretically homogeneous -Fold endonuclease. RRl [pACYCfofcJM, pRRSfo/cJi?] were grown in 6L of 2 x TY containing 20μg Tc/ml and 50 μg/Ap ml at 37°C to A$oo = 0.8. and then induced overnight with 1 mM IPTG. The cells were harvested by centrifugation and then resuspended in 250 ml of buffer A [10 mM Tris.phosphate (pH 8.0), 7 mM 2- mercaptoethanol, 1 mM EDTA, 10% glycerol] containing 50 mM NaCl. The cells were disrupted at maximum intensity on a Branson Sonicator for 1 hr at 4°C. The sonicated cells were centrifuged at 12,000 g for 2 hr at 4°C. The supernatant was then diluted to IL with buffer A containing 50 mM NaCl. The supernatant was loaded onto a 10 ml phosphocellulose (Whatman) column pre-equilibrated with buffer A containing 50 mM NaCl. The column was washed with 50 ml of loading buffer and the protein was eluted with a 80-ml total gradient of 0.05M to 0.5M NaCl in buffer A. The fractions were monitored by A 280 absorption and analyzed by electrophoresis on SDS (0.1%)-polyacrylamide (12%) gels (Laemmli, Nature, 222:680-685, 1970). Proteins were stained with coomassie blue. Restriction endonuclease activity of the fractions were assayed using pTZ19R as substrate. The fractions containing Fokl were pooled and fractionated with ammonium sulfate. The 50-70% ammonium sulfate fraction contained the Fokl endonuclease. The precipitate was resuspended in 50 ml of buffer A containing 25 mM NaCl and loaded onto a DEAE column. Fokl does not bind to DEAE while many contaminating proteins do. The flow-through was concentrated on a phosphocellulose column. Further purification was achieved using gel filtration (AcA 44) column. The Fokl was purified to electrophoretic homogeneity using this procedure. SDS (0.1%) polyacrylamide (12%) gel electrophoresis profiles of protein species present at each stage of purification are shown in Figure 3. The sequence of the first ten amino acids of the purified enzyme was determined by protein sequencing. The determined sequence was the same as that predicted from the nucleotide sequence. Crystals of this purified enzyme have also been grown using PEG 4000 as the precipitant. Fokl endonuclease was purified further using AcA44 gel filtration column. Example IV Analysis of FokIR endonuclease by trypsin cleavage in the presence of DNA substrate. Trypsin is a serine protease and it cleaves at the C-terminal side of lysine and arginine residues. This is a very useful enzyme to study the domain structure of proteins and enzymes. Trypsin digestion of Fokl in the presence of its substrate, d-5'-CCTCTGGATGCTCTC-3• (SEQ ID NO: 10): 5'-GAGAGCATCCAGAGG-3' (SEQ ID NO: 11) was carried out with an oligonucleotide duplex to Fokl molar ratio of 2.5:1. Fokl (200 μg) was incubated with the oligonucleotide duplex in a volume 180 μl containing 10 mM Tris.HCl, 50 mM NaCl, 10% glycerol and 10 mM MgCl 2 at RT for 1 hr. Trypsin (20 μl, 0.2 mg/ml) was added to the mixture. Aliquots (28 μl) from the reaction mixture were removed at different time intervals and quenched with excess trypsin inhibitor, antipain. The tryptic fragments were purified by reversed-phase HPLC and their N-terminus sequence determined using an automatic protein sequenator from Applied Biosystems. The time course of trypsin digestion of Fokl endonuclease in the presence of 2.5 molar excess of oligonucleotide substrate and 10 mM MgCl 2 is shown in Figure 4. At the 2.5 min time point only two major fragments other than the intact Fokl were present, a 41 kDa fragment and a 25 kDa fragment. Upon further trypsin digestion, the 41 kDa fragment degraded into a 30 kDa fragment and 11 kDA fragment. The 25 kDa fragment appeared to be resistant to any further trypsin digestion. This fragment appeared to be less stable if the trypsin digestion of Fokl - oligo complex was carried out in the absence of MgCl 2 . Only three major fragments (30 kDa, 25 kDa and 11 kDa) were present at the 160 min time point. Each of these fragments (41 kDa, 30 kDa, 25 kDa and 11 kDa) was purified by reversed-phase HPLC and their N-terminal amino acid sequence were determined (Table I) . By comparing these N-terminal sequences to the predicted sequence of Fokl , the 41 kDa and 25 kDa fragments were identified as N-terminal and C- terminal fragments, respectively. In addition, the 30 kDa fragment was N-terminal. Example V Isolation of DNA binding tryptic fragments of FoJcI endonuclease using oligo dT-cellulose affinity column. The DNA binding properties of the tryptic fragments were analyzed using an oligo dT-cellulose column. Fokl (160 μg) was incubated with the 2.5 molar excess oligonucleotide duplex [d-5 1 - CCTCTGGATGCTCTC(A) 15 -3' (SEQ ID NO: 14): 5'GAGAGCATCCAGAGG(A)i 5 -3' (SEQ ID NO: 15)] in a volume of 90 μl containing 10 mM Tris.HCl (pH 8) , 50 mM NaCl, 10% glycerol and 10 mM MgCl 2 at RT for 1 hr. Trypsin (10 μl, 0.2 mg/ml) was added to the solution to initiate digestion. The ratio of trypsin to Fokl (by weight) was 1:80. Digestion was carried out for 10 min to obtain predominantly 41 kDa N-terminal fragment and 25 kDa C-terminal fragments in the reaction mixture. The reaction was quenched with large excess of antipain (10 μg) and diluted in loading buffer [10 mM.Tris HCl (pH 8.0), 1 mM EDTA and 100 mM MgCl 2 ] to a final volume of 400 μl. The solution was loaded onto a oligo dT- cellulose column (0.5 ml, Sigma, catalog #0-7751) pre-equilibrated with the loading buffer. The breakthrough was passed over the oligo dT-cellulose column six times. The column was washed with 5 ml of loading buffer and then eluted twice with 0.4 ml of 10 mM Tris.HCl (pH 8.0), 1 mM EDTA. These fractions contained the tryptic fragments that were bound to the oligonucleotide DNA substrate. The tryptic fragment bound to the oligo dT-cellulose column was analyzed by SDS-polyacrylamide gel electrophoresis. In a separate reaction, the trypsin digestion was carried out for 160 min to obtain predominantly the 30 kDa, 25 kDa and 11 kDa fragments in the reaction mixture. Trypsin digestion of Fokl endonuclease for 10 min yielded the 41 kDa N-terminal fragment and 25 kDa C-terminal fragments as the predominant species in the reaction mixture (Figure 5, Lane 3) . When this mixture was passed over the oligo dT-cellulose column, only the 41 kDa N-terminal fragment is retained by the column suggesting that the DNA binding property of Fokl endonuclease is in the N- terminal 2/3's of the enzyme. The 25 kDa fragment is not retained by the oligo dT-cellulose column. Trypsin digestion of Fokl - oligo complex for 160 min yielded predominantly the 30 kDa, 25 kDa and 11 kDa fragments (Figure 5, Lane 5) . When this reaction mixture was passed over oligo dT-cellulose column, only the 30 kDa and 11 kDa fragments were retained. It appears these species together bind DNA and they arise from further degradation of 41 kDa N-terminal fragment. The 25 kDa fragment was not retained by oligo dT-cellulose column. It also did not bind to DEAE and thus could be purified by passage through a DEAE column and recovering it in the breakthrough volume. Fokl (390 μg) was incubated with 2.5 molar excess of oligonucleotide duplex [d-5 1 - CTCTGGATGCTCTC-3 (SEQ ID NO: 10)':5'- GAGAGCATCCAGAGG-3 ' (SEQ ID NO: 11)] in a total volume of 170 μl containing 10 mM Tris.HCl (pH 8) , 50 mM NaCl and 10% glycerol at RT for l hr. Digestion with trypsin (30 μl; 0.2 mg/ml) in the absence of MgCl 2 was for 10 min at RT to maximize the yield of the 41 kDa N-terminal fragment. The reaction was quenched with excess antipain (200 μl) . The tryptic digest was passed through a DEAE column. The 25 kDa of C-terminal fragment was recovered in the breakthrough volume. All the other tryptic fragments (41 kDa, 30 kDa and 11 kDa) were retained by the column and were eluted with 0.5M NaCl buffer (3 x 200 μl). In a separate experiment, the trypsin digestion of Fokl -oligo complex was done in presence of 10 mM MgCl 2 at RT for 60 min to maximize the yield of 30 kDa and 11 kDa fragments. This purified fragment cleaved non-specifically both unmethylated DNA substrate (pTZ19R; Figure 6) and methylated DNA substrate (pACYCfo/JM) in the presence of MgCl 2 . These products are small, indicating that it is relatively non-specific in cleavage. The products were dephosphorylated using calf intestinal phosphatase and rephosphorylated using polynucleotide kinase and [ Y - 32 P] ATP. The 32 P-labeled products were digested to mononucleotides using DNase I and snake venom phosphodiesterase. Analysis of the mononucleotides by PEI-cellulose chromatography indicates that the 25 kDa fragment cleaved preferentially phosphodiester bonds 5* to G>A»T-C. The 25 kDa C- terminal fragment thus constitutes the cleavage domain of Fokl endonuclease. The 41 kDa N-terminal fragment - oligo complex was purified by agarose gel electrophoresis. Fokl endonuclease (200 μg) was incubated with 2.5 molar excess of oligonucleotide duplex, [d-5' - CCTCTGGATGCTCTC-3• (SEQ ID NO: 10) : 5'- GAGAGCATCCAGAGG-3' (SEQ ID NO:11)] in a volume of 180 μl containing 10 mM Tris.HCl (pH 8.0), 50 mM NaCl and 10% glycerol at RT for 1 hr. Tracer amounts of 32 P-labeled oligonucleotide duplex was incorporated into the complex to monitor it during gel electrophoresis. Digestion with trypsin (20 μl; 0.2 mg/ml) was for 12 min at RT to maximize the yield of the 41 kDa N-terminal fragment. The reaction was quenched with excess antipain. The 41 kDa N- terminal fragment - oligo complex was purified by agarose gel electrophoresis. The band corresponding to the complex was excised and recovered by electroelution in a dialysis bag (- 600 μl) . Analysis of the complex by SDS-PAGE revealed 41 kDa N-terminal fragment to be the major component. The 30 kDa N-terminal fragment and the 11 kDa C-terminal fragment were present as minor components. These together appeared to bind DNA and co-migrate with the 41 kDa N-terminal fragment-oligo complex. The binding specificity of the 41 KDa N- terminal fragment was determined using gel mobility shift assays. Example VI Gel Mobility shift assays The specific oligos (d-5'-CCTCTGGATGCTCTC- 3' (SEQ ID NO: 10) and d-5'-GAGAGCATCCAGAGG-3' (SEQ ID NO: 11)) were 5'- 32 P-labeled in a reaction mixture of 25 μl containing 40 mM Tris.HCl(pH7.5) , 20mM MgCl 2 ,50 mM NaCl, 10 mM DTT, 10 units of T4 polynucleotide kinase (from New England Biolabs) and 20 μCi[ γ - 32 P] ATP (3000 Ci/m ol) . The mixture was incubated at 37°C for 30 min. The kinase was inactivated by heating the reaction mixture to 70°C for 15 min. After addition of 200 μl of water, the solution was passed through Sephadex G-25 (Superfine) column (Pharmacia) to remove the unreacted [ Y - 32 P] ATP. The final concentration of labeled single-strand oligos were 27 μM. The single-strands were then annealed to form the duplex in 10 mM Tris.HCl (pH 8.0), 50 mM NaCl to a concentration of 12 μM. 1 μl of the solution contained ~ 12 picomoles of oligo duplex and - 50 x 10 3 cpm. The non-specific oligos (d-5'~ TAATTGATTCTTAA-3' (SEQ ID NO: 12) and d-5'- ATTAAGAATCAATT-3' (SEQ ID NO:13)) were labeled with [ γ - 32 P]ATP and polynucleotide kinase as described herein. The single-stranded oligos were annealed to yield the duplex at a concentration of 12μM. 1 μl of the solution contained ~ 12 picomoles of oligo duplex and - 25 x lθ 3 cpm. The non-specific oligos (d-5'-TAATTGATTCTTAA-3' (SEQ ID NO: 12) and d-5'- ATTAAGAATCAATT-3• (SEQ ID NO: 13)) were labeled with [ Y _ 3 2p-j ATP and polynucleotide Kinase as described herein. The single-strand oligos were annealed to yield the duplex at a concentration of 12μM. 1 μl of the solution contained 42 picomdes of oligo duplex and -25xl0 3 cpm. 10 μl of 41 kDa N-terminal fragment-oligo complex (- 2 pmoles) in 10 mM Tris.HCl, 50 mM NaCl and 10 mM MgCl 2 was incubated with 1 μl of 3 p- labeled specific oligonucleotide duplex (or 3 p- labeled non-specific oligonucleotide duplex) at 37°C for 30 min and 120 min respectively. 5 μl of 75% glycerol was added to each sample and loaded on a 8% nondenaturing polyacrylamide gel. Electrophoresis was at 300 volts in TBE buffer until bromophenol blue moved - 6 cm from the top of the gel. The gel was dried and autoradiographed. The complex readily exchanged 32 P-labeled specific oligonucleotide duplex that contained the Fokl recognition site as seen from the gel mobility shift assays (Figure 7) . It did not, however, exchange the 32 P-labeled non-specific oligonucleotide duplex that did not contain the Fokl recognition site. These results indicate that all the information necessary for sequence-specific recognition of DNA are encoded within the 41 kDa N- terminal fragment of Fokl . Example VII Analysis of Fokl by trypsin cleavage in the absence of DNA substrate. A time course of trypsin digestion of Fokl endonuclease in the absence of the DNA substrate is shown in Figure 8. Initially, Fokl cleaved into a 58 kDa fragment and a 8 kDa fragment. The 58 kDa fragment did not bind DNA substrates and is not retained by the oligo dT-cellulose column. On further digestion, the 58 kDa fragment degraded into several intermediate tryptic fragments. However, the complete trypsin digestion yielded only 25 kDa fragments (appears as two overlapping bands). Each of these species (58 kDa, 25 kDa and 8 kDa) were purified by reversed phase HPLC and their amino terminal amino acid sequence determined (Table I) . Comparison of the N-terminal sequences to the predicted Fokl sequence revealed that the 8 kDa fragment to be N-terminal and the 58 kDa fragment to be C-terminal. This further supports the conclusion that N-terminus of Fokl is responsible for the recognition domain. Sequencing the N-terminus of the 25 kDa fragments revealed the presence of two different components. A time course of trypsin digestion of Fokl endonuclease in a the presence of a non-specific DNA substrate yielded a profile similar to the one obtained when trypsin digestion of Fokl is carried out in absence of any DNA substrate. Example VIII Cleavage specificity of the 25 kDa C-terminal tryptic fragment of Fokl The 25 kDa C-terminal tryptic fragment of Fokl cleaved pTZ19R to small products indicating non-specific cleavage. The degradation products were dephosphorylated by calf intestinal phosphatase and 3 P-labeled with the polynucleotide kinase and [τ- 3 P]ATP. The excess label was removed using a Sephadex G-25 (Superfine) column. The labeled products were then digested with 1 unit of pancreatic DNase I (Boehringer-Mannhei ) in buffer containing 50 mM Tris.HCl(pH7.6) , lOmM MgCl 2 at 37°C for 1 hr. Then, 0.02 units of snake venom phosphodiesterase was added to the reaction mixture and digested at 37°C for 1 hr. Example IX Functional domains in Fokl restriction endonuclease. Analysis of functional domains of Fokl (in the presence and absence of substrates) using trypsin was summarized in Figure 9. Binding of DNA substrate by Fokl was accompanied by alteration in the structure of the enzyme. This study supports that presence of two separate protein domains within this enzyme: one for sequence-specific recognition and the other for endonuclease activity. The results indicate that the recognition domain is at the N-terminus of the Fokl endonuclease, while the cleavage domain is probably in the C-terminus third of the molecule. Examples Relating to Construction of Insertion Mutants (X-XIV) The complete nucleotide sequence of the Fokl RM system has been published by various laboratories (Looney et al.. Gene 80: 193-208, 1989 & Kita et al., J. Biol.Chem. 264: 5751-56, 1989). Experimental protocols for PCR are described, for example, in Skoglund et al... Gene 88:1-5, 1990 and in Bassing et al.. Gene 113:83-88, 1992. The procedures for cell growth and purification of the mutant enzymes are similar to the ones used for the wild-type Fokl (Li et al., Proc. Nat'l. Acad. Sci. USA 89:4275-79, 1992). Additional steps which include Sephadex G-75 gel filtration and Heparin- Sepharose CL-6B column chromatography were necessary to purify the mutant enzymes to homogeneity. Example X Mutagensis of Spel Site at Nucleotide 162 within the fokIR Gene The two step PCR technique used to mutagenize one of the Spel sites within the fokIR gene is described in Landt et al.. Gene 96: 125-28, 1990. The three synthetic primers for this protocol include: 1) the mutagenic primer (5'-TCATAA TAGCAACTAATTCTTTTTGGATCTT-3' ) (see SEQ ID NO:24) containing one base mismatch within the Spel site; 2) the other primers each of which are flanked by restriction sites Clal (5'-CCATCGATATAGCCTTTTTTATT- 3') (see SEQ ID NO:25) and XJbaJ (5 » - GCTCTAGAGGATCCGGAGGT-3') (see SEQ ID NO:26), respectively. An intermediate fragment was amplified using the Xbal primer and the mutagenic primer during the first step. The Clal primer was then added to the intermediate for the second step PCR. The final 0.3 kb PCR product was digested with Xbal /Clal to generate cohesive ends and gel- purified. The expression vector (pRRSfofcJi?) was cleaved with Xbal / Clal . The large 4.2 kb fragment was then gel-purified and ligated to the PCR fragment. The recombinant DNA was transfected into competent E. coli RRl[pACYCfoΛJW] cells. After tetracycline and ampicillin antibiotic selection several clones were picked, and their plasmid DNA was examined by restriction analysis. The Spel site mutation was confirmed by sequencing the plasmid DNA using Sanger's sequencing method (Sanger et al. Proc. Natl. Acad. Sci. USA 74: 5463-67, 1977). Example XI Construction of four for seven) codon Insertion Mutants The PCR-generated DNA containing a four (or seven) codon insertion was digested with a Spel/Xmal and gel-purified. The plasmid, pRRSfoJJR from Example X was cleaved with Spel/Xmal , and the large 3.9 kb fragment was gel-purified and ligated to the PCR product. The recombinant DNA was transfected into competent RRl[pACYCfo-*JM] cells, and the desired clones identified as described in Example X. The plasmids from these clones were isolated and sequenced to confirm the presence of the four (or seven) codon insertion within the fokIR gene. in particular, the construction of the mutants was performed as follows: (1) There are two Spel sites at nucleotides 162 and 1152, respectively, within the fokIR gene sequence. The site at 1152 is located near the trypsin cleavage site of Fokl that separates the recognition and cleavage domains. In order to insert the four (or seven) codons around this region, the other Spel site at 162 was mutagenized using a two step PCR technique (Landt et al. Gene 96:125-28, 1990). Introduction of this Spel site mutation in the fokΣR gene does not affect the expression levels of the overproducer clones. (2) The insertion of four (or seven) codons was achieved using the PCR technique. The mutagenic primers used in the PCR amplification are shown in Figure 11. Each primer has a 21 bp complementary sequence to the fokIR gene. The 5' end of these primers are flanked by Spel sites. The codons for KSEL and KSELEEK repeats are incorporated between the Spel site and the 21 bp complement. Degenerate codons were used in these repeats to circumvent potential problems during PCR amplification. The other primer is complementary to the 3' end of the fokIR gene and is flanked by a Xmal site. The PCR-generated 0.6 kb fragments containing the four (or seven) codon inserts digested with Spel /Xmal and gel-purified. These fragments were substituted into the high expression vector pRRS-ofcJR to generate the mutants. Several clones of each mutant identified and their DNA sequence confirmed by Sanger's dideoxy chain termination method (Sanger et al. Proc. Natl. Acad. Sci. USA 74.5463-67 1977). Upon induction with 1 mM isopropyl β-D- thiogalactoside (IPTG) , the expression of mutant enzymes in these clones became most prominent at 3 hrs as determined by SDS/PAGE. This was further supported by the assays for the enzyme activity. The levels of expression of the mutant enzymes in these clones were much lower compared to the wild- type Fokl . IPTG induction for longer times resulted in lower enzyme levels indicating that the mutant enzymes were actively degraded within these clones. This suggests that the insertion of four (or seven) codons between the recognition and cleavage domains of Fokl destabilizes the protein conformation making them more susceptible to degradation within the cells. SDS/PAGE profiles of the mutant enzymes are shown in Figure 12. Example XII Preparation of DNA Substrates with a Single Fokl Site Two substrates, each containing a single Fokl recognition site, were prepared by PCR using pTZ19R as the template. Oligonucleotide primers, 5'-CGCAGTGTTATCACTCAT-3' and 5'-CTTGGTTGAGTACTCACC- 3' (see SEQ ID NO:27 and SEQ ID NO:28, respectively), were used to synthesize the 100 bp fragment. Primers, 5'-ACCGAGCTCGAATTCACT-3' and 5'- GATTTCGGCCTATTGGTT-3• (see SEQ ID NO:29 and SEQ ID NO:30, respectively), were used to prepare the 256 bp fragment. Individual strands within these substrates were radiolabled by using the corresponding 32 P-labeled phosphorylated primers during PCR. The products were purified from low- melting agarose gel, ethanol precipitated and resuspended in TE buffer. Example XIII Analysis of the Seguence Specificity of the Mutant Enzymes The agarose gel electrophoretic profile of the cleavage products of pTZ19R DNA by Fokl and the mutants are shown in Figure 13A. They are very similar suggesting that insertion of four (or seven) codons in the linker region between the recognition and cleavage domains does not alter its DNA sequence specificity. This was further confirmed by using 3 P-labeled DNA substrates (100 bp and 256 bp) each containing a single Fokl site. Substrates containing individual strands labeled with 32 P were prepared as described in Example XII. Fokl cleaves the 256 bp substrate into two fragments, 180 bp and 72 bp, respectively (Figure 13B) . The length of the fragments was calculated from the 32 P-labeled 5' end of each strand. The autoradiograph of the agarose gel is shown in Figure 13C. Depending on which strand carries the 32 P-label in the substrate, either 72 bp fragment or 180 bp fragment appears as a band in the autoradiograph. The mutant enzymes reveal identical agarose gel profiles and autoradiograph. Therefore, insertion of four (or seven) codons between the recognition and cleavage domains does not alter the DNA recognition mechanism of Fokl endonuclease. Example XIV Analysis of the Cleavage Distances from the Recognition Site by the Mutant Enzymes To determine the distance of cleavage by the mutant enzymes, their cleavage products of the 32 P-labeled substrates were analyzed by PAGE (Figure 14) . The digests were analyzed alongside the sequencing reactions of pTZ19R performed with the same primers used in PCR to synthesize these substrates. The cleavage pattern of the 100 bp fragment by Fokl and the mutants are shown in Figure 14A. The cut sites are shifted from the recognition site on both strands of the substrates in the case of the mutants, as compared to the wild-type enzyme. The small observable shifts between the sequencing gel and the cleavage products are due to the unphosphorylated primers that were used in the sequencing reactions. On the 5'-GGATG-3* strand, both mutants cut the DNA 10 nucleotides away from the site while on the 5•-CATCC-3' strand they cut 14 nucleotides away from the recognition site. These appear to be the major cut sites for both the mutants. A small amount of cleavage similar to the wild-type enzyme was is also observed. The cleavage pattern of the 256 bp fragment is shown in Figure 14B. The pattern of cleavage is shown in Figure 14B. The pattern of cleavage is similar to the 100 bp fragment. Some cleavage is seen 15 nucleotides away from the recognition site on the 5'-CATCC-3 • strand in the case of the mutants. The multiple cut sites for the mutant enzymes could be attributed to the presence of different conformations in these proteins. Or due to the increased flexibility of the spacer region between the two domains. Depending on the DNA substrate, some variation in the intensity of cleavage at these sites was observed. This may be due to the nucleotide sequence around these cut sites. Naturally occurring Type IIS enzymes with multiple cut sites have been reported (Szybalski et al., Gene 100:13-26, 1991). TABLE 1 Amino-terminal sequences of Fokl fragments from trypsin digestion Fragment Amino-terminal sequence DNA SEQ ID substrate NO 8 kDa VSKIRTFG*VQNPGKFENLKRWQVFDRS - 16 58 kDa SEAPCDAIIQ 17 25 kDa QLVKSELEEK + 18 41 kDa VSKIRTFGWV 19 30 kDa VSKIRTFGWV 19 11 kDa FTRVPKRVY 20 TABLE 2 Class-II restriction endonucleases (ENases-IIS) as listed .Kel;Ro2- . Isoschizomers are listed in CO parentheses (very recently discovered or incompletely characterized isoschizomers are in footnotes i-k) . An ENase-IIS is defined as an enzyme which cuts at precise distance away from its recognition site, without cleaving this site. Enzymes in lines 36 and 37 ((Bsml. Bsr. six Asp, and BscCI) do not fit this definition 30 because one of the two cuts is within the recognition site, but they were included because several of their rn properties and applications are quite similar to those of enzymes 1-35. ENase in line 29 (NgoVII) was not 3 described, but the M.Nαo VIII MTase appears to match the Hphl) . Genes coding for Eco571 and Fokl were cloned (Ja3? Wjp . ENases Ecαl. Eco571 and Gsul (and their isoschizomers?) require or are stimulated by AdoMet. The recognition sequences ae asymmetric [with exception of those marked S (in bp column) which display a partial symmetry (which might be incidental) ] , and are oriented so that the cut sites are to the right (downstream) of them. E.g., GGATC(M) 4 (line 1), indicates that the cut on the upper strand is between 4th CCTAG(N) 5 and 5th nt beyond C; on the lower strand the cut is between 5th and 6th nt beyond G. Length of the recognition site is given in bp, and the symbols -(- or - below it indicate whether the purified enzyme cuts (+) or does not (-) ss DNA. N, A, or G or T; R, A or G, C or T. c As deduced from cut sites (see column 3). n.d., not determined. d Strains which produce the specified Enases-IIS. e Other unrelated Enases produced by the same strain. c f MTases-IIS isolated from the same strain. Genes bbvIM. eco571M. foklM. hqalM. mboIIM and sfaNIM (coding 2} for M.BbvI. M.Eco571. M.FokI f M.H al. M.MboII. and M.SfaNI. respectively; Sz3) were cloned (Ba4; BoQ: Ja3; C * Win . MTases with the same site specificity, but produced by another strain, are in parentheses, rn Methylated based (m 5 C or mN 6 A) ae shown in brackets (as C-5 or A-N6, respectively) . m _-ϋj 9 A, Amersha Buchler, Buckinghamshire (U.K.); B, BRL/Life Technologies, Gaithersburg, MD; F, ESP Fermentas, 33 2328 Vilnius, Lithuania (U.S.S.R.) (some also available from N) ; G, Anglian Biotechnology, Colchester ^ (u.k.); 1, IBI/International Biotechnology, New Haven, CT; M, Boehringer/Mannheim, Mannheim (F.R.G.); N, £ New England Biolabs, Beverly, MA; P, PL-Pharmacia, Milwaukee, WI; S, Stratagene, La Jolla, Ca; U, Dept. of Microbiology, University of Gdansk, Gdansk (Poland) ; Y, NY Biolabs, New York, NY; Z, see American Chemical Society Biotech buyers' Guide (1991). Parentheses indicate that the ENase is produced, but not yet commercially available. " These enzymes do not formally belong to class IIS (see footnotes) . They are also deεignated IIT (Kel) ; (N)-l indicates a cut within the recognition site in the lower strand (see arrowhead). Cuts unknown (See Ro2) . Also 28 additional ENases: Cfr561. Eco42 Eco511. Eco951. Eco971. EcolOll. Eco 1201. Eco 1271. Eco 1291. Eco 1551. Eco 1561. Eco 1571. Eco 1621. 1851 Eco 1911 Eco 2031. Eco 2051. Eco 2171. Eco 2251. Eco 2391. Eco 2401. Eco 2411. Eco 2461. Eco 2471. pal. Sau 121. which have the same recognition sequence, but for most of them cuts are unknown (see fto2) . Ppal has the same cut as Eco 311 (ne3) . Also additional isochizomers Asp26HI. Asp27HI f Asp36HI Asp40HI. AspSOHI (R02- . and BscCI (from Bacillus sp. 2G). from Szybalski et al. [Gene 100:14-26 (1991)]. m m 03 SEQUENCE LISTING (1) GENERAL INFORMATION: (i) APPLICANT: Chandrasegaran, Srinivasan (ii) TITLE OF INVENTION: Functional Domains in Fokl Restriction Endonuclease (iii) NUMBER OF SEQUENCES: 40 (iv) CORRESPONDENCE ADDRESS: (A) ADDRESSEE: Cushman, Darby & Cushman (B) STREET: 1100 New York Ave. , N.W. (C) CITY: Washington (D) STATE: D.C. (E) COUNTRY: USA (F) ZIP: 20005-3918 (v) COMPUTER READABLE FORM: (A) MEDIUM TYPE: Floppy disk (B) COMPUTER: IBM PC compatible (C) OPERATING SYSTEM: PC-DOS/MS-DOS (D) SOFTWARE: Patentln Release #1.0, Version #1.25 (vi) CURRENT APPLICATION DATA: (A) APPLICATION NUMBER: (B) FILING DATE: (C) CLASSIFICATION: (viii) ATTORNEY/AGENT INFORMATION: (A) NAME: Kokulis, Paul N. (B) REGISTRATION NUMBER: 16,773 (C) REFERENCE/DOCKET NUMBER: PNK/4130/122364/CLB (ix) TELECOMMUNICATION INFORMATION: (A) TELEPHONE: 202-861-3503 (B) TELEFAX: 202-822-0944 (C) TELEX: 6714627 CUSH (2) INFORMATION FOR SEQ ID NO:l: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 5 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (xi) SEQUENCE DESCRIPTION: SEQ ID Nl GGATG (2) INFORMATION FOR SEQ ID NO:2: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 5 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (xi) SEQUENCE DESCRIPTION: SEQ ID K CCTAC (2) INFORMATION FOR SEQ ID NO:3: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 35 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (ix) FEATURE: (A) NAME/KEY: CDS (B) LOCATION: 18..35 SUBSTfTUTESHEET(RULE26) (Xi) SEQUENCE DESCRIPTION: SEQ ID NO:3: CCATGGAGGT TTAAAAT ATG AGA TTT ATT GGC AGC 35 Met Arg Phe lie Gly Ser 1 5 (2) INFORMATION FOR SEQ ID NO:4: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 6 amino acids (B) TYPE: amino acid (D) TOPOLOGY: linear (ii) MOLECULE TYPE: protein (xi) SEQUENCE DESCRIPTION: SEQ ID NO:4: Met Arg Phe lie Gly Ser 1 5 (2) INFORMATION FOR SEQ ID NO:5: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 30 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (xi) SEQUENCE DESCRIPTION: SEQ ID NO:5: ATACCATGGG AATTAAATGA CACAGCATCA 30 (2) INFORMATION FOR SEQ ID NO:6: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 42 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) ( ix) FEATURE : (A) NAME/KEY: CDS (B) LOCATION: 22..42 (xi) SEQUENCE DESCRIPTION: SEQ ID NO:6: AGGATCCGG AGGTTTAAAA T ATG GTT TCT AAA ATA AGA ACT 42 Met Val Ser Lys lie Arg Thr 1 5 (2) INFORMATION FOR SEQ ID NO:7: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 7 amino acids (B) TYPE: amino acid (D) TOPOLOGY: linear (ii) MOLECULE TYPE: protein (Xi) SEQUENCE DESCRIPTION: SEQ ID NO:7: Met Val Ser Lys lie Arg Thr 1 5 (2) INFORMATION FOR SEQ ID NO:8: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 35 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (Xi) SEQUENCE DESCRIPTION: SEQ ID NO:8: TAGGATCCTC ATTAAAAGTT TATCTCGCCG TTATT 35 SUBS UTΕ SHEET (RULE 26) (2) INFORMATION FOR SEQ ID NO:9: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 7 amino acids (B) TYPE: amino acid (D) TOPOLOGY: linear (ii) MOLECULE TYPE: protein (xi) SEQUENCE DESCRIPTION: SEQ ID NO:9: sn Asn Gly Glu lie Asn Phe 1 5 (2) INFORMATION FOR SEQ ID NO:10: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 15 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (xi) SEQUENCE DESCRIPTION: SEQ ID NO:10: CCTCTGGATG CTCTC 15 (2) INFORMATION FOR SEQ ID NO:11: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 15 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (Xi) SEQUENCE DESCRIPTION: SEQ ID NO:11: GAGAGCATCC AGAGG 15 (2) INFORMATION FOR SEQ ID NO:12: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 14 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (Xi) SEQUENCE DESCRIPTION: SEQ ID NO:12: TAATTGATTC TTAA 14 (2) INFORMATION FOR SEQ ID NO:13: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 14 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (xi) SEQUENCE DESCRIPTION: SEQ ID NO:13: ATTAAGAATC AATT 14 (2) INFORMATION FOR SEQ ID NO:14: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 30 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (xi) SEQUENCE DESCRIPTION: SEQ ID NO:14: CCTCTGGATG CTCTCAAAAA AAAAAAAAAA 30 (2) INFORMATION FOR SEQ ID NO:15: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 30 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (xi) SEQUENCE DESCRIPTION: SEQ ID NO:15: GAGAGCATCC AGAGGAAAAA AAAAAAAAAA 30 (2) INFORMATION FOR SEQ ID NO:16: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 29 amino acids (B) TYPE: amino acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: peptide (xi) SEQUENCE DESCRIPTION: SEQ ID NO:16: Val Ser Lys lie Arg Thr Phe Gly Xaa Val Gin Asn Pro Gly 1 5 10 Lys Phe Glu Asn Leu Lys Arg Val Val Gin Val Phe Asp Arg 15 20 25 Ser (2) INFORMATION FOR SEQ ID NO:17: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 10 amino acids (B) TYPE: amino acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear ( ii) MOLECULE TYPE : peptide (Xi) SEQUENCE DESCRIPTION: SEQ ID NO:17: Ser Glu Ala Pro Cys Asp Ala lie lie Gin 1 5 10 (2) INFORMATION FOR SEQ ID NO:18: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 10 amino acids (B) TYPE: amino acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: peptide (xi) SEQUENCE DESCRIPTION: SEQ ID NO:18: Gin Leu Val Lys Ser Glu Leu Glu Glu Lys 1 5 10 (2) INFORMATION FOR SEQ ID NO:19: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 10 amino acids (B) TYPE: amino acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: peptide (xi) SEQUENCE DESCRIPTION: SEQ ID NO:19: Val Ser Lys lie Arg Thr Phe Gly Trp Val 1 5 10 (2) INFORMATION FOR SEQ ID NO:20: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 9 amino acids (B) TYPE: amino acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: peptide (Xi) SEQUENCE DESCRIPTION: SEQ ID NO:20: Phe Thr Arg Val Pro Lys Arg Val Tyr 1 5 (2) INFORMATION FOR SEQ ID NO:21: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 3 amino acids (B) TYPE: amino acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: peptide (Xi) SEQUENCE DESCRIPTION: SEQ ID NO:21: Glu Glu Lys 1 (2) INFORMATION FOR SEQ ID NO:22: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 4 amino acids (B) TYPE: amino acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: peptide (Xi) SEQUENCE DESCRIPTION: SEQ ID NO:22: Lys Ser Glu Leu 1 (2) INFORMATION FOR SEQ ID NO:23: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 7 amino acids (B) TYPE: amino acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: peptide (xi) SEQUENCE DESCRIPTION: SEQ ID NO:23: Lys Ser Glu Leu Glu Glu Lys 1 5 (2) INFORMATION FOR SEQ ID NO:24: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 25 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (xi) SEQUENCE DESCRIPTION: SEQ ID NO:24: TAGCAACTAA TTCTTTTTGG ATCTT 25 (2) INFORMATION FOR SEQ ID NO:25: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 23 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (xi) SEQUENCE DESCRIPTION: SEQ ID NO:25: CCATCGATAT AGCCTTTTTT ATT 23 (2) INFORMATION FOR SEQ ID NO:26: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 20 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (Xi) SEQUENCE DESCRIPTION: SEQ ID NO:26: GCTCTAGAGG ATCCGGAGGT 20 (2) INFORMATION FOR SEQ ID NO:27: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 18 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (Xi) SEQUENCE DESCRIPTION: SEQ ID NO:27: CGCAGTGTTA TCACTCAT 18 (2) INFORMATION FOR SEQ ID NO:28: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 18 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (Xi) SEQUENCE DESCRIPTION: SEQ ID NO:28: CTTGGTTGAG TACTCACC 18 (2) INFORMATION FOR SEQ ID NO:29: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 18 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (Xi) SEQUENCE DESCRIPTION: SEQ ID NO:29: ACCGAGCTCG AATTCACT 18 (2) INFORMATION FOR SEQ ID NO:30: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 18 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (xi) SEQUENCE DESCRIPTION: SEQ ID NO:30: GATTTCGGCC TATTGGTT 18 (2) INFORMATION FOR SEQ ID NO:31: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 579 amino acids (B) TYPE: amino acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: peptide (Xi) SEQUENCE DESCRIPTION: SEQ ID NO:31: Met Val Ser Lys lie Arg Thr Phe Gly Trp Val Gin Asn Pro 1 5 10 Gly Lys Phe Glu Asn Leu Lys Arg Val Val Gin Val Phe Asp 15 20 25 Arg Asn Ser Lys Val His Asn Glu Val Lys Asn lie Lys lie 30 35 40 Pro Thr Leu Val Lys Glu Ser Lys lie Gin Lys Glu Leu Val 45 50 55 Ala lie Met Asn Gin His Asp Leu lie Tyr Thr Tyr Lys Glu 60 65 70 Leu Val Gly Thr Gly Thr Ser lie Arg Ser Glu Ala Pro Cys 75 80 Asp Ala lie lie Gin Ala Thr lie Ala Asp Gin Gly Asn Lys 85 90 95 Lys Gly Tyr lie Asp Asn Trp Ser Ser Asp Gly Phe Leu Arg 100 105 110 Trp Ala His Ala Leu Gly Phe lie Glu Tyr lie Asn Lys Ser 115 120 125 Asp Ser Phe Val lie Thr Asp Val Gly Leu Ala Tyr Ser Lys 130 135 140 Ser Ala Asp Gly Ser Ala lie Glu Lys Glu lie Leu lie Glu 145 150 Ala lie Ser Ser Tyr Pro Pro Ala lie Arg lie Leu Thr Leu 155 160 165 Leu Glu Asp Gly Gin His Leu Thr Lys Phe Asp Leu Gly Lys 170 175 180 Asn Leu Gly Phe Ser Gly Glu Ser Gly Phe Thr Ser Leu Pro 185 190 195 Glu Gly lie Leu Leu Asp Thr Leu Ala Asn Ala Met Pro Lys 200 205 210 Asp Lys Gly Glu lie Arg Asn Asn Trp Glu Gly Ser Ser Asp 215 220 Lys Tyr Ala Arg Met lie Gly Gly Trp Leu Asp Lys Leu Gly 225 230 235 Leu Val Lys Gin Gly Lys Lys Glu Phe lie lie Pro Thr Leu 240 245 250 Gly Lys Pro Asp Asn Lys Glu Phe lie Ser His Ala Phe Lys 255 260 265 lie Thr Gly Glu Gly Leu Lys Val Leu Arg Arg Ala Lys Gly 270 275 280 Ser Thr Lys Phe Thr Arg Val Pro Lys Arg Val Tyr Trp Glu 285 290 Met Leu Ala Thr Asn Leu Thr Asp Lys Glu Tyr Val Arg Thr 295 300 305 Arg Arg Ala Leu lie Leu Glu lie Leu lie Lys Ala Gly Ser 310 315 320 Leu Lys lie Glu Gin lie Gin Asp Asn Leu Lys Lys Leu Gly 325 330 335 Phe Asp Glu Val lie Glu Thr lie Glu Asn Asp lie Lys Gly 340 345 350 Leu lie Asn Thr Gly lie Phe lie Glu lie Lys Gly Arg Phe 355 360 Tyr Gin Leu Lys Asp His lie Leu Gin Phe Val lie Pro Asn 365 370 375 Arg Gly Val Thr Lys Gin Leu Val Lys Ser Glu Leu Glu Glu 380 385 390 Lys Lys Ser Glu Leu Arg His Lys Leu Lys Tyr Val Pro His 395 400 405 Glu Tyr lie Glu Leu lie Glu lie Ala Arg Asn Ser Thr Gin 410 415 420 Asp Arg lie Leu Glu Met Lys Val Met Glu Phe Phe Met Lys 425 430 Val Tyr Gly Tyr Arg Gly Lys His Leu Gly Gly Ser Arg Lys 435 440 445 Pro Asp Gly Ala lie Tyr Thr Val Gly Ser Pro lie Asp Tyr 450 455 460 Gly Val lie Val Asp Thr Lys Ala Tyr Ser Gly Gly Tyr Asn 465 470 475 Leu Pro lie Gly Gin Ala Asp Glu Met Gin Arg Tyr Val Glu 480 485 490 Glu Asn Gin Thr Arg Asn Lys His lie Asn Pro Asn Glu Trp 495 500 Trp Lys Val Tyr Pro Ser Ser Val Thr Glu Phe Lys Phe Leu 505 510 515 Phe Val Ser Gly His Phe Lys Gly Asn Tyr Lys Ala Gin Leu 520 525 530 Thr Arg Leu Asn His lie Thr Asn Cys Asn Gly Ala Val Leu 535 540 545 Ser Val Glu Glu Leu Leu lie Gly Gly Glu Met lie Lys Ala 550 555 560 Gly Thr Leu Thr Leu Glu Glu Val Arg Arg Lys Phe Asn Asn 565 570 Gly Glu lie Asn Phe 575 (2) INFORMATION FOR SEQ ID NO:32: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 11 amino acids (B) TYPE: amino acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: peptide (xi) SEQUENCE DESCRIPTION: SEQ ID NO:32: Lys Gin Leu Val Lys Ser Glu Leu Glu Glu Lys 1 5 10 (2) INFORMATION FOR SEQ ID NO:33: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 33 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (Xi) SEQUENCE DESCRIPTION: SEQ ID NO:33: AAGCAACTAG TCAAAAGTGA ACTGGAGGAG AAG 33 (2) INFORMATION FOR SEQ ID NO:34: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 13 amino acids (B) TYPE: amino acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: peptide (xi) SEQUENCE DESCRIPTION: SEQ ID NO:34: Leu Val Lys Ser Glu Leu Lys Ser Glu Leu Glu Glu Lys 1 5 10 (2) INFORMATION FOR SEQ ID NO:35: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 42 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (Xi) SEQUENCE DESCRIPTION: SEQ ID NO:35: GGACTAGTCA AATCTGAACT TAAAAGTGAA CTGGAGGAGA AG 42 (2) INFORMATION FOR SEQ ID NO:36: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 16 amino acids (B) TYPE: amino acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: peptide (Xi) SEQUENCE DESCRIPTION: SEQ ID NO:36: Leu Val Lys Ser Glu Leu Glu Glu Lys Lys Ser Glu Leu Glu 1 5 10 Glu Lys 15 (2) INFORMATION FOR SEQ ID NO:37: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 51 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (Xi) SEQUENCE DESCRIPTION: SEQ ID NO:37: GGACTAGTCA AATCTGAACT TGAGGAGAAG AAAAGTGAAC TGGAGGAGAA G 51 (2) INFORMATION FOR SEQ ID NO:38: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 4 amino acids (B) TYPE: amino acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: peptide (xi) SEQUENCE DESCRIPTION: SEQ ID NO:38: Asn Phe Xaa Xaa 1 (2) INFORMATION FOR SEQ ID NO:39: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 27 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (Xi) SEQUENCE DESCRIPTION: SEQ ID NO:39: TTGAAAATTA CTCCTAGGGG CCCCCCT 27 (2) INFORMATION FOR SEQ ID NO:40: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 23 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (xi) SEQUENCE DESCRIPTION: SEQ ID NO:40: GGATGNNNNNNNNNNNNNNNNNN 23 * * * * * All publications mentioned hereinabove are hereby incorporated by reference. While the foregoing invention has been described in some detail for purposes of clarity and understanding, it will be appreciated by one skilled in the art that various changes in form and detail can be made without departing from the true scope of the invention.

Claims: WHAT IS CLAIMED IS: 1. An isolated DNA segment encoding the recognition domain of a Type IIS endonuclease which contains the sequence-specific recognition activity of said Type IIS endonuclease. 2. The DNA segment of claim 1 wherein said Type IIS endonuclease is Fokl restriction endonuclease. 3. The DNA segment of claim 2 which encodes amino acids 1-382 of the Fokl restriction endonuclease. 4. An isolated DNA segment encoding the catalytic domain of a Type IIS endonuclease which contains the cleavage activity of said Type IIS endonuclease. 5. The DNA segment of claim 4 wherein said Type IIS endonuclease is Fokl restriction endonuclease. 6. The DNA segment of claim 5 which encodes amino acids 383-578 of the Fokl restriction endonuclease. 7. An isolated protein consisting essentially of the N-terminus of the Fokl restriction endonuclease which protein has the sequence-specific recognition activity of said endonuclease. 8. An isolated protein consisting essentially of the C-terminus of the FoJcI restriction endonuclease which protein has the cleavage activity of said endonuclease. 9. A DNA construct comprising: (i) a first DNA segment encoding the catalytic domain of a Type IIS endonuclease which contains the cleavage activity of said Type IIS endonuclease; (ii) a second DNA segment encoding a sequence-specific recognition domain other than the recognition domain of said Type IIS endonuclease; and (iii) a vector wherein said first DNA segment and said second DNA segment are operably linked to said vector so that a single protein is produced. 10. The DNA construct according to claim 9 wherein said Type IIS endonuclease is Fokl restriction endonuclease. 11. The DNA construct according to claim 10 wherein said recognition domain is selected from the group consisting of: zinc finger motifs, homeo domain motifs, DNA binding domains of repressors, DNA binding domains of oncogenes and naturally occurring sequence-specific DNA binding proteins that recognize >6 base pairs. 12. A procaryotic cell comprising: (i) a first DNA segment encoding the catalytic domain of a Type IIS endonuclease which contains the cleavage activity of said Type IIS endonuclease; (ii) a second DNA segment encoding a sequence-specific recognition domain other than the recognition domain of said Type IIS endonuclease; and (iii) a vector wherein said first DNA segment and said second DNA segment are operably linked to said vector so that a single protein is produced. 13. A hybrid restriction enzyme comprising the catalytic domain of a Type IIS endonuclease which contains the cleavage activity of said Type IIS endonuclease covalently linked to a recognition domain of a protein other than said Type IIS endonuclease. 14. The hybrid restriction enzyme of claim 13 wherein said recognition domain which comprises part of said hybrid restriction enzyme is selected from the group consisting of: zinc finger motifs, homeo domain motifs, DNA binding domains of repressors, DNA binding domains of oncogenes and naturally occurring sequence-specific DNA binding proteins that recognize >6 base pairs. 15. A DNA construct comprising: (i) a first DNA segment encoding the catalytic domain of a Type IIS endonuclease which contains the cleavage activity of said Type IIS endonuclease; (ii) a second DNA segment encoding a sequence-specific recognition domain other than the recognition domain of said Type IIS endonuclease; (iii) a third DNA segment comprising one or more codons, wherein said third DNA segment is inserted between said first DNA segment and said second DNA segment; and (iv) a vector wherein said first DNA segment, said second DNA segment and said third DNA segment are operably linked to said vector so that a single protein is produced. 16. The DNA construct according to claim 15 wherein said Type IIS endonuclease is Fokl restriction endonuclease. 17. The DNA construct according to claim 16 wherein said third DNA segment consists essentially of four codons. 18. The DNA construct according to claim 17 wherein said four codons of said third DNA segment are inserted at nucleotide 1152 of the gene encoding said endonuclease. 19. The DNA construct according to claim 16 wherein said third DNA segment consists essentially of 7 codons. 20. The DNA construct according to claim 19 wherein said 7 codons of said third DNA segment are inserted at nucleotide 1152 of the gene encoding said endonuclease. 21. The DNA construct according to claim 16 wherein said recognition domain is selected from the group consisting of: zinc finger motifs, homeo domain motifs, DNA binding domains of repressors, DNA binding domains of oncogenes and naturally occurring sequence-specific DNA binding proteins that recognize >6 base pairs. 22. A procaryotic cell comprising: (i) a first DNA segment encoding the catalytic domain of a Type IIS endonuclease which contains the cleavage activity of said Type IIS endonuclease; (ii) a second DNA segment encoding a sequence-specific recognition domain other than the recognition domain of said Type IIS endonuclease; (iii) a third DNA segment comprising one or more codons, wherein said third DNA segment is inserted between said first DNA segment and said second DNA segment; and (iv) a vector wherein said first DNA segment, said second DNA segment, and said third DNA segment are operably linked to said vector so that a single protein is produced. 23. The procaryotic cell of claim 22 wherein said third DNA segment consists essentially of four codons. 24. The procaryotic cell of claim 22 wherein said third DNA segment consists essentially of seven codons. 25. An isolated protein produced by the procaryotic cell of claim 22. 26. An isolated DNA segment encoding the N-terminus of a Type IIS endonuclease which contains the sequence-specific recognition activity of said Type II endonuclease, said Type II endonuclease being Fokl restriction endonuclease and having a molecular weight of about 41 kilodaltons as measured by SDS-polyacrylamide gel electrophoresis. 27. An isolated DNA segment encoding the C-terminus of a Type IIS endonuclease which contains the cleavage activity of said Type IIS endonuclease, said Type II endonuclease being Fokl restriction endonuclease and having a molecular weight of about 25 kilodaltons as determined by SDS-polyacrylamide gel electrophoresis. 28. An isolated protein consisting essentially of the N-terminus of the Fok restriction endonuclease which protein has the sequence-specific recognition activity of said endonuclease and which protein is amino acids 1-382 of said Fok restriction endonuclease. 29. An isolated protein consisting essentially of the C-terminus of the Fokl restriction endonuclease which protein has the nuclease activity of said endonuclease and which protein is amino acids 383-578 of said Fokl restriction endonuclease.

Inventors: CHANDRASEGARAN SRINIVASAN, CHANDRASEGARAN, SRINIVASAN
Applicants: UNIV JOHNS HOPKINS, THE JOHNS-HOPKINS UNIVERSITY
Application year: 1994
Main classification: C12N9
IPC codes: C07K14, C12N1, C12N9, C12N15, C12P21, C12Q1, C12R1